Tips for removing residual solder?

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Mr.Whipple
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Tips for removing residual solder?

Post by Mr.Whipple » Thu Mar 13, 2003 11:57 am

Hi,<p>I'm trying to remove a stubborn thin layer of solder from several delicate, gold colored parts.<p>Aside from desoldering wick, is there anything else you would recommend that could completely remove trace amounts of solder? <p>Thanks.

chessman
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Re: Tips for removing residual solder?

Post by chessman » Thu Mar 13, 2003 12:00 pm

A really cool desolder iron with the built in pump.<p>Jameco has a neat electric pump that doesn't have an iron for $26.95 Jameco<p>Circuit Specialists has a cheap de-soldering iron w/pump for $159 http://www.web-tronics.com/dessysjfon15.html<p>Also, for $10 Radio Shack has a de-soldering iron with a bulb the you pump by hand.<p>[ March 13, 2003: Message edited by: chessman ]</p>

Ron H
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Re: Tips for removing residual solder?

Post by Ron H » Thu Mar 13, 2003 12:57 pm

Short of some sort of electrolysis process or mechanical abrading, I don't think you can remove all traces of solder. Solder works by alloying itself with the metal it is adhering to. I don't think you can remove it by applying heat and trying to wick/scrape/suction it off.

bodgy
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Re: Tips for removing residual solder?

Post by bodgy » Thu Mar 13, 2003 2:51 pm

Try applying flux and then some solder to the iron and use fine braid solder wick.<p>The flux I have in mind is quite expensive and will either be in a flux pen dispenser or a runny jelly type in a syringe - I don't know the US brands too well, but the ones I'm thinking of are made by Multicore.<p>Don't use plumbers flux.<p>Paint on flux is great for all solder removal, I use it for SMT removals plus plenty of solder.<p>If you look at the Farnell website they may have a picture of the syringe based flux, if you look at the RS components website they now only stock the flux pens or massive spray cans of the stuff.<p>Colin
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haklesup
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Re: Tips for removing residual solder?

Post by haklesup » Thu Mar 13, 2003 3:35 pm

Assuming the base metal is Gold (although Copper should give similar selectivity)Copper does etch more readily than Gold both are destroyed by anything with Nitric acid in it.<p>A solder etch bath can be made from 75%(by Vol) Acetic Acid and 25% (by vol) Hydrogen Peroxide (H2O2)(30%). Now that peroxide is industrial strength, not the 0.5% [correction 3%]stuff you buy in the store. It will burn your skin instantly (use gloves and have a water wash ready). It is a little hard to get though. A similar recipe calls for 1:1 ratio of the two chemicals. A third etch uses 1:1:1 Amonium Hydroxide, Peroxide and Water. You can try it with houshold peroxide but you will probably need to heat it up and wait a lot longer if it even works.<p>Gold etches usually contain Nitric and HCL acids or Nitric and H2O2. I am not completely sure if the solder etch is selective to not etch Gold but I think it would be OK. I have a variety of other gold etches too but that is not what you want.<p>Try putting a similar amount of solder on some gold fingers of a trash PCB and try the etch before you do it on the real thing.<p>If you cannot get this stuff, I can recommend some Semiconductor Failure Analysis labs who will do it for you for a fee.<p>[ March 13, 2003: Message edited by: haklesup ]</p>

ad5mb
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Re: Tips for removing residual solder?

Post by ad5mb » Thu Mar 13, 2003 4:27 pm

RonH is right. The solder flows into gaps between molecules in the wires that are soldered. it fills in spaces in the contacts. You would have to melt these parts and centrifuge the material to separate the solder from the gold.

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haklesup
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Re: Tips for removing residual solder?

Post by haklesup » Thu Mar 13, 2003 4:53 pm

More precisely, the gold forms a thin intermetallic layer that is an alloy of the two metals (actually 3 or more since solder is already an alloy). The thickness of this layer depends on the grain size and excat composition of the base metal (gold or gold alloy) and the temperature it was applied etc. but it is usually very thin in the order of a few microns. <p>Anyway, there is no mechanical means to remove the solder 100% because the alloy (gold-solder)will always remain. Complete removal requires a chemical etch like I described. This is likely to change the surface's finish because micro-pits will exist where grains of the alloy were removed but since gold is soft, you could probably polish it to a consistant fininh in a seperate step or re-plate the contacts with new gold.<p>Obviously you wouldn't etch a complete PC board if you wanted to clean one part but for most epoxy or glass encapsulated components, the etch should be safe on the component body. <p>How much do you really want these clean, anyhow?

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Re: Tips for removing residual solder?

Post by Ron H » Thu Mar 13, 2003 8:31 pm

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr>Originally posted by Mr.Whipple:
Hi,<p>I'm trying to remove a stubborn thin layer of solder from several delicate, gold colored parts.<p>Aside from desoldering wick, is there anything else you would recommend that could completely remove trace amounts of solder? <p>Thanks.<hr></blockquote><p>
Note that Mr. Whipple said gold COLORED. If they are real gold, they might survive a chemical etch. If not...<p>Ron

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